1. Field of the Invention
The present invention relates to a liquid-jet recording head having an ejection-energy-generating element, and more particularly to a recording head which can solve the problem caused by the heat from the ejection-energy-generating element. The present invention also relates to a recording apparatus having the above-mentioned recording head, and more particularly to a recording apparatus which can be miniaturized and simplified.
2. Related Background Art
In known liquid-jet recording apparatuses, liquid is ejected in minute liquid droplets driven by a pressure change in the liquid path caused by the strain of a piezoelectric element, or further, the ejected liquid droplets are deflected by the additional provision of a pair of electrodes. In other proposed apparatuses, liquid is ejected by the driving force of bubbles generated by abrupt heat generation in a heating element in the liquid path. There are further various proposals regarding liquid ejection.
Among these, the types of ejection of a recording liquid by use of heat energy mentioned last, as disclosed in U.S. Pat. No. 4,723,129 and U.S. Pat. No. 4,740,796, is regarded as being particularly useful in liquid-jet recording apparatuses because the method enables the high-density arrangement of the ejection openings as well as high-speed recording.
In such recording methods, the change of temperature of the recording liquid caused by the drive of the ejection-energy generating elements or by the heat transferred from the drive-signal transmitting circuit can sometimes be a serious factor. The reason is that a recording liquid will change its properties, such as surface tension and viscosity, depending on the temperature, and such a change will affect the ejected quantity, the feeding rate, etc. of the recording liquid. The temperature rise of the recording liquid is remarkable when a heat-generating element is employed. This temperature rise depends on the temperature rise of the substrate of the recording head where the heat-generating element is provided. For controlling the temperature of recording liquids, systems have been employed in which the temperature rise of the substrate (hereinafter referred to as "a heat-generating substrate") is prevented.
One of the systems, for example, is based on spontaneous cooling (air-cooling) in which a heat-generating substrate is attached onto a heat-conductive substrate so that the superfluous portion of the heat energy generated by the heat-generating substrate may be released through the heat-conductive substrate to the surrounding atmosphere.
There is literature regarding heat problems. Japanese Patent Publication No. Sho-56-9429 (1981) discloses a Peltier element, provided in addition to a heat-energy generating element, to allow bubbles to constrict after their formation by nuclear boiling, thus extinguishing the bubbles. U.S. Pat. No. 4,723,129 discloses use of a heat energy generating element simultaneously exhibiting a Peltier effect also. These elements, however, are directed to bubbles per se, and do not based directly on the technical idea regarding a heat-generating substrate. Japanese Patent Laid-open Application No. Sho-59-138472 (1984) discloses a perforation construction of a substrate for the supply of liquid from the back face to its front face adjacent to a common liquid chamber for the purpose of stable liquid supply from the common chamber to a plurality of liquid paths. This publication, however, recognizes nothing about the problems caused by heat. The reason is clear from the fact that the construction disclosed by the Patent Publication includes a very small contact region area between the liquid supply paths and the substrate so that the thermal variation is not influential.
Anyway, a recording head of a liquid-jet recording apparatus employing liquid ejection energy, and in particular, employing heat energy, involves the problem that, when high-density recording such as solid printing is practiced particularly at a high velocity by a high-frequency drive, the temperature of the recording head rises to cause abnormal bubbling, resulting in difficulty in the formation of normal liquid droplets, and deterioration of the quality of recording caused by a variation of dot diameter at a temperature higher than a certain level T.sub.1.
To meet the problems, the recording is simply stopped when the temperature of the recording head rises to a certain temperature T.sub.2 which is lower than temperature T.sub.1 until the temperature of the head falls, or otherwise the liquid temperature is lowered by conducting preliminary ejection as disclosed in British Patent No. 2,165,855, and thereafter the recording is re-started. However, such interruption of recording for a long time offsets the advantage of high speed recording.
The above-mentioned phenomenon of temperature rise is especially remarkable in recording heads made of a low-thermal-conductivity material such as a plastic. A construction employing a high-thermal-conductivity material for cooling is not suitable for miniaturization of the head because of the required large volume of the heat radiation substrate to secure sufficient heat capacity.
On the other hand, air-cooling types of heads involve problems that the recording is liable to be affected by the environment and that the temperature cannot easily be controlled stably and effectively. In this type of cooling, heat is accumulated increasingly with the lapse of time, causing a temperature rise of the liquid, a change of ejected liquid droplet diameter and ejecting rate, etc. with time, and non-uniformity of recording concentration from the beginning to the end of the recording, which may not sufficiently satisfy the need for a stable recording of high quality.